Hypoxemia and hyperoxemia are frequent after acute subarachnoid hemorrhage (aSAH) and are associated with an increase in morbidity and mortality. Among the pulmonary complications causing oxygen derangements, acute respiratory distress syndrome (ARDS) seems to be crucial, with a reported incidence ranging from 11 to 50%. Methods We designed a multicentric, retrospective cohort study in tree intensive care in Europe. We collected data between January 2009 and December 2017. We included adult

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... ents (≥18 years) with a diagnosis of aSAH. Hypoxemia was defined as PaO 2 <60mmHg, mild hyperoxemia as PaO 2 >120mmHg, and severe hyperoxemia as PaO 2 >200mmHg. The primary aim of this study was to assess the incidence of episodes of hypoxemia, hyperoxemia, and the oxygen variability values (calculated as the daily difference between the highest and the lowest arterial partial pressure of oxygen (PaO 2 )) during the first week after the intensive care unit (ICU) admission. Secondary aims included the evaluation of the incidence of ARDS according to the Berlin criteria, and the assessment of the effect of oxygen derangements on patients' outcomes. Results 855 patients fulfilled the inclusion criteria. 6.4% of the patients presented at least one episode of hypoxemia (PaO 2 <60mmHg), 56.6% of mild hyperoxemia (PaO 2 >120mmHg), and 16.8% of severe hyperoxemia (PaO 2 >200mmHg). The cumulative incidence of ARDS resulted in 2.2% on the first day since ICU admission, 3.2% by three days, and 3.6% by seven days. A lower Glasgow Coma Scale score (GCS) at admission, longer duration of mechanical ventilation, higher PaO 2 variability, hypoxemia, and ARDS occurrence were independently associated with poor outcome. Conclusions Hypoxemia and hyperoxemia episodes are frequent in the first 7-days of ICU stay after aSAH, whereas ARDS has a low incidence. The severity of aSAH but also ARDS occurrence, oxygenation parameters, None Abbreviations ABG: arterial blood gas analysis; ARDS: acute respiratory distress syndrome; aSAH: aneurismal subarachnoid hemorrhage; cmH 2 O: centimeters of water; EVD: external ventricular drain; FiO 2 : inhaled oxygen fraction;